This invention relates to pneumatic tires wherein the structural members are held together in the building of the tire by a new butt-splicing technique, and a method of using such a technique in the building of a tire.
In the building of pneumatic tires, the structural elements, such as the carcass plies, are laid down in one or more sections on a tire building drum Since it is important that the ends of these structural elements are strongly connected to one another, so that the ends of the plies will not separate in the expansion step in the building of a tire, it is common in the prior art to lay down the plies in an overlapping configuration known in the art as an overlapping splice. The overlapping splice holds the ends of the plies together in the tire building process
The use of the overlapping splice, especially in the carcass plies, has the disadvantage, however, that in the regions where the plies overlap, there is an uneven expansion of the ply in the expansion step because of the large number of reinforcing members in the overlap area, as compared with the number of reinforcing members in the rest of the tire construction Accordingly, the splicing, although necessary in the building of the tire, causes the tire to have a certain amount of nonuniformity which may cause sidewall undulations (bulges and valleys) in the tire. Such nonuniformity has a tendency to cause a vibration and noise when the tire is running.
In an attempt to eliminate overlapping splices in a tire, the prior art has attempted to build tires using butt splices wherein the ends of the carcass and belt plies of the tire are laid down abutting one another, rather than overlapping. In the prior art butt splices, the ends of the plies where they abut are held together during the building of the tire by an overlapping section of adhesively coated fabric. Although an improvement over the overlap splice, the fabric used in the butt splice still adds substantially to the mass of the tire in the splice area, and may cause restriction of the expansion of the carcass ply and does not totally eliminate distortion in the splice area.
It is the purpose of the present invention to provide a tire using a butt splice whereby the splicing material is of minimum gauge and produces minimum distortion in the splice area and which substantially and economically improves tire uniformity and substantially eliminates sidewall undulations and gaps.
Also, a method is provided to produce a butt splice which will not open during tire shaping and produces minimum distortion in the splice area, while not adding appreciably to the gauge and mass nor detracting from the durability of the tire.